Data reported in: Effects of ozone isotopologue formation on the clumped-isotope composition of atmospheric O2

• Main Author: Yeung, Laurence
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Zenodo 2021
• Subjects: ice core
• Online Access: https://dx.doi.org/10.5281/zenodo.4763876; https://zenodo.org/record/4763876

Tropospheric 18 O 18 O is an emerging proxy for past tropospheric ozone and free-tropospheric temperatures. The basis of these applications is the idea that isotope-exchange reactions in the atmosphere drive 18 O 18 O abundances toward isotopic equilibrium. However, previous work used an offline box-model framework to explain the 18 O 18 O budget, approximating the interplay of atmospheric chemistry and transport. This approach, while convenient, has poorly characterized uncertainties. To investigate these uncertainties, and to broaden the applicability of the 18 O 18 O proxy, we developed a scheme to simulate atmospheric 18 O 18 O abundances (quantified as ∆ 36 values) online within the GEOS-Chem chemical transport model. These results are compared to both new and previously published atmospheric observations from the surface to 33 km. Simulations using a simplified O 2 isotopic equilibration scheme within GEOS-Chem show quantitative agreement with measurements only in the middle stratosphere; modeled ∆ 36 values are too high elsewhere. Investigations using a comprehensive model of the O-O 2 -O 3 isotopic photochemical system and proof-of-principle experiments suggest that the simple equilibration scheme omits an important pressure dependence to ∆ 36 values: the anomalously efficient titration of 18 O 18 O to form ozone. Incorporating these effects into the online ∆ 36 calculation scheme in GEOS-Chem yields quantitative agreement for all available observations. While this previously unidentified bias affects the atmospheric budget of 18 O 18 O in O 2 , the modeled change in the mean tropospheric ∆ 36 value since 1850 C.E. is only slightly altered; it is still quantitatively consistent with the ice-core ∆ 36 record, implying that the tropospheric ozone burden increased less than ~40% over the twentieth century. : Funding provided by: National Science Foundation Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001 Award Number: AGS-2002422Funding provided by: National Science Foundation Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001 Award Number: AGS-2002414Funding provided by: National Aeronautics and Space Administration Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000104 Award Number: NNX17AE36GFunding provided by: David and Lucile Packard Foundation Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000008 Award Number: